1. Field of the Invention
The present invention generally relates to semiconductor processing in a plasma treatment apparatus, particularly to a method of reducing a floating potential of a substrate upon film formation.
2. Description of the Related Art
In capacity-coupled plasma CVD, a floating voltage is generated on a substrate placed on a substrate processing base while film is being formed. This substrate voltage remains in the substrate after the film forming process has completed, and may sometimes cause the substrate to be attracted to the substrate processing base, in which case a problem will occur in the subsequent process of transferring the substrate.
The sticking force that applies between the wafer and electrode is expressed by the formula below:
  F  =                    ɛ        0            ⁢              ɛ        r            ⁢              SV        w        2                    2      ⁢              d        2            
Here, F (N) indicates the sticking force, ∈0 (F/m) indicates the dielectric constant in vacuum, ∈r indicates the specific dielectric constant of anodic oxidation, S (m2) indicates the wafer area, Vw (V) indicates the floating potential of the wafer, and d (m) indicates the thickness of film generated by anodic oxidation. Based on the above formula, the sticking force can be decreased by lowering Vw.
Traditionally, the method of applying RF power continuously after the film forming process has completed to remove electric charges from the substrate has been used to reduce the sticking force of the wafer and electrode.
However, the aforementioned method presents problems in that it cannot lower the substrate voltage sufficiently if an increased number of substrates are processed, or under different substrate conditions such as when different types of fine processing have been applied to the substrate or depending on whether or not an insulation film is formed on the back of the substrate, in which case the substrate will still be attracted to the substrate processing base and proper transfer will be prevented.